Conventionally, electrical discharge machines including an electrode guide for supporting an electrode near a workpiece have been known (see Patent Literature 1, for example). In the electrical discharge machine described in Patent Literature 1, the front end of an electrode projected downward by a predetermined length (50 mm) from the bottom endface of an electrode guide is made to abut against the workpiece surface. Thereafter, with the electrode guide fixed, the electrode is moved up by a length (49.5 mm) slightly shorter than the aforementioned predetermined length. Then, the electrode guide and the electrode are moved down by a length (49 mm) slightly shorter than the above length. As a result, the electrode guide is positioned a predetermined distance (1 mm) apart from the workpiece surface with the front end of the electrode projected a predetermined length (0.5 mm) from the bottom endface of the electrode guide.
However, in the positioning method according to above Patent Document 1, the electrode guide is positioned at a point a predetermined distance away from the workpiece surface without taking into account the position of the workpiece, so that when hole machining is implemented on the surface of a workpiece that is tilted, the electrode guide may interfere with the workpiece surface.